Belgian Pat. No. 821,163, granted Apr. 17, 1975 on an application filed on my behalf, and also my pending U.S. patent application Ser. No. 561,147 filed Mar. 24, 1975, disclose a broad genus of antibacterial agents of the formula I, wherein R.sup.1 is an acyl group of an organic carboxylic acid. Additionally, the same broad genus of compounds is the subject matter of Iranian Pat. No. 12574, issued Jan. 12, 1975; African and Malagasy Republic Pat. No. 04798, issued Dec. 12, 1974; Lebanese Pat. No. 4088, issued Dec. 5, 1974; Paraguayan Pat. No. 2512, issued Apr. 8, 1975; Vietnamese Pat. No. 2647, issued Jan. 29, 1975 and now abandoned; and Zaire Pat. No. 1697/74, issued Mar. 12, 1975. However, it has now been discovered that the compound of the formula I, wherein R.sup.1 is a 2-[4-hydroxy-1,5-naphthyridine-3-carboxamido]-2-[4-hydroxyphenyl]acetyl group, which is not specifically disclosed in said Belgian Pat. No. 821,163 or said pending United States patent application Ser. No. 561,147 shows especially valuable antibacterial properties. In particular, the compound of the formula I, wherein R.sup.1 is 2-[4-hydroxy-1,5-naphthyridine-3-carboxamido]-2-[4-hydroxyphenyl]acetyl possesses important advantages over the structurally most-closely related analogues disclosed in the said Belgian patent and the said United States patent application. ##STR1##